Wobble information recording method, information recording medium, and recording and reproduction method and apparatus thereof

ABSTRACT

An optical disk and a method for identifying the optical disk are provided which make it possible to identify a recording system of the optical disk easily in a short time by a recording and reproduction apparatus when a groove-recording system and a land-recording system are both employed in one kind of optical disk, for, example, a BD-R. Specifically, the polarity upon reproducing the wobble information is made to be the same in both of the optical disk of groove-recording system and the optical disk of land-recording system. The recording system of the optical disk that shows the same wobble polarity irrespective of the recording system can be easily detected by finding a tracking polarity that can recognize the wobble information by changing the tracking polarity, whereby the start-up time of the recording and reproduction apparatus can be shortened.

This is a divisional of application Ser. No. 10/577,926, which is theNational Stage of International Application No. PCT/JP2005/008838, filedMay 10, 2005.

TECHNICAL FIELD

The present invention is related to a method for recording wobbleinformation of an information recording medium such as an optical diskso that a polarity of detected wobble information is the sameirrespective of recording system, and an information recording mediumwherein the wobble information is recorded according to the method.

Further, the present invention is related to a method and apparatus forrecording and reproducing information using the information recordingmedium.

BACKGROUND OF THE INVENTION

Conventionally, CD-R/RW or DVD-R/RW/RAM have been used as a write-onceor an rewritable optical disk and recently demand for a DVD-R/RW/RAM hasbeen increased since a DVD recorder has widely prevailed for recordingTV broadcasts. A guide groove is provided in these optical disks andreference signals for synchronizing a linear velocity upon recording andreproducing and optional address information signals are recorded inthese optical disks by “wobble” signals which are a meander of the guidegroove. A recording and reproduction apparatus for such an optical diskrecords and reproduces information by detecting the wobble signals toadjust the linear velocity and detecting the address if the addressinformation is added to the optical disk. Of the above optical disks,the DVD-RAM employs a recording system (or a recording mode) which maybe called as “land & groove” recording system according to whichrecording and reproduction of information are carried out on both ofland portions (that are faces far from a light used for recording andreproduction) and the groove portions (that are faces near to the light)of the guide groove, and all the other optical disks employ a grooverecording system according to which the recording and reproduction ofinformation are carried out only on the groove portions (that are facesnear to the light used for recording and reproduction) of the guidegroove.

Recently, an optical disk whose recording density is higher than the DVDhas been developed. In general, information is recorded on andreproduced from the optical disk by an incident light for recording andreproduction which light passes through a transparent layer which may becalled as a “substrate.” The thickness of the substrate through whichthe light for recording and reproduction passes is 0.6 mm for the DVD.The study has been made for further thinning the thickness of thesubstrate into about 0.1 mm and thereby using a light with a shortwavelength for recording and reproduction. As a result, a recordableBlu-ray Disc (BD) has been developed.

In the case where the thickness of the substrate is thin such as 0.1 mm,it is difficult to form the guide groove in the sheet having a thicknessof 0.1 mm and to form the recording layer on its surface. For thisreason, an approach for producing the Blu-ray Disc is made wherein theguide groove is formed in a substrate of a 1.1 mm thickness which is tobe positioned at the side (rear side) that is not irradiated with thelight for recording and reproducing and the recording layer is formed onthe guide groove followed by forming a cover layer of a 0.1 mmthickness. In this case, the light for recording and reproducing isapplied from the side of the cover layer.

When the recording layer is formed by sputtering a material forrecording layer onto the surface of the rear-side substrate, therecording layer can be deposited and formed so that the thickness of therecording layer in the groove portions (the top surface of the guidegroove) is almost the same as that in the land portions (the bottomsurface of the guide groove) viewed from the cover layer side where thelight for recording and reproducing is applied. Therefore, in this case,the portions that present a better recording and reproductioncharacteristics, which is generally the groove portions, can be used forrecording and reproduction.

Further, there is a method for applying an organic dye by a spin-coatmethod as a method for forming the recording layer. For example,Japanese Patent Kokai (Laid-Open) Publication No. 2003-109246(A)describes a method for producing a write-once optical disk whichincludes forming the recording layer by applying the organic dye on therear-side substrate by the spin-coat method and then forming the coverlayer. However, according to the spin coat method, the organic dyepreferentially deposits in the groove portions (concaved portions) ofthe substrate. As a result, the recording layer is formed thickly in theland portions when viewed from the cover layer side. Therefore, sincethe recording film is easily formed in the land portions in this case,it is preferable that the land portions are used for recording andreproduction.

SUMMARY OF THE INVENTION

As described above, an appropriate recording system depends on themethod for forming the recording film. However, when tracking isconducted by, for example, a push-pull method, tracking characteristicsobtained when using the groove portions as the recording layer isreversal of those when using the land portion as the recording layer.Similarly, a polarity of wobble signals obtained in reproduced signalswhen reproducing the signals recorded in the groove portions is reversalof a polarity of wobble signals obtained in reproduced signals whenreproducing the signals recorded in the land portions.

In a recording and reproduction apparatus, a circuit for tracking isgenerally separated from a circuit for detecting wobble signals. Forthis reason, when it is desired that a single recording and reproductionapparatus accepts two types of optical disks, one being of the grooverecording system, and the other being of the land-recording system, itis necessary to detect whether the portions to be used for recording isthe groove portions or the land portions and to detect the wobble signalpolarity for a loaded optical disk, which results in a problem that alonger time is required for start-up.

In order to resolve this problem, the present inventors propose that thepolarity obtained upon reproducing the wobble signals is made the samein both of the information recording medium of land-recording system andthe information recording medium of groove-recording system.Specifically, the polarity of wobble signals formed in the opticalrecording medium which employs one recording system is made mirrorreverse of that formed in the optical recording medium which employs theother recording system. More specifically, the physical direction of thewobble (specifically, right and left of starting direction of thewobble, that is, whether the wobble starts its first wobble deviationtowards the inner side or the outer side of the medium) in the case ofthe groove-recording system is reversed in the wobble in the case of theland-recording system so that the polarity of the wobble signals in thecase of the land-recording system is made to be the same as the polarityof the wobble signals in the case of the groove-recording system.Herein, the phrase “the wobble starts its first wobble deviation towardsthe inner side of a medium” means that a starting point of the wobble ispositioned at the innermost of the medium (a position nearer to thecenter in the case of a disk) relative to a position where a wobbleamplitude is zero and the wobble starts from the starting point as shownin FIG. 6. The phrase “the wobble starts its first wobble deviationtowards the outer side of a medium” means that a starting point of thewobble is positioned at the outermost of the medium relative to aposition where the wobble amplitude is zero and the wobble starts fromthe starting point as shown in FIG. 7. Both of the wobbles shown inFIGS. 6 and 7 are monotone wobbles. Timing and address information byMSK (Minimum Shift Keying) modulation and HMW (Harmonic Modulated Wave)modulation are optionally incorporated into the monotone wobble.

Thus, the present invention provides a method for recording wobbleinformation of an information recording medium which includes:

selecting a recording system; and

forming a guide groove having wobble information wherein the wobblestarts its first wobble deviation towards the inner side of the mediumin the case where the selected recording system is a groove-recordingsystem, or a guide groove having wobble information wherein the wobblestarts its first wobble deviation towards the outer side of the mediumin the case where the selected recording system is a land-recordingsystem. This is particularly applicable to an optical disk on and fromwhich information is recorded and reproduced with a light. This methodmakes it possible that the polarity of the wobble signals of theinformation recording medium of the groove-recording system is the sameas that of the information recording medium of the land-recordingsystem. According to this method, an information recording medium ofgroove-recording system, wherein a wobble starts its first wobbledeviation towards the inner side of the medium in a guide groove havingwobble information, and an information recording medium ofland-recording system, wherein a wobble starts its first wobbledeviation towards the outer side of the medium in a guide groove havingwobble information can be obtained.

Further, the present invention provides a method for recording wobbleinformation of a multi-layer information recording medium having aplurality of recording layers, which includes making the wobble polaritythat is detected from all the recording layers to be the same, and amulti-layer information recording medium having a plurality of recordinglayers wherein wobble information is recorded according to this method.In such an information recording medium, the wobble starts its firstwobble deviation towards the inner side or the outer side of the mediumin a guide groove having wobble information for each recording layerdepending on a recording system of the each recording layer. Herein, theterms “a guide groove for a certain recording layer” means a groove forguiding a light used for recording information on the certain recordinglayer and reproducing the information from the certain recording layer.

Furthermore, the present invention provides a method for recordinginformation on and reproducing information from an information recordingmedium of the present invention, which includes judging a trackingpolarity peculiar to a loaded information recording medium(particularly, an optical disk), based on the result whether or notwobble information is detected from wobble signals under a fixedtracking polarity. Further, the present invention provides a recordingand reproduction apparatus which is used for carrying out this method.

In these recording and reproduction method and apparatus, the default ofthe tracking polarity may be preferably one for a groove-recordingsystem. Since many optical disks conventionally employ thegroove-recording system, it may be considered that many unspecifiedoptical disks also employ the groove-recording system. For this reason,the default of the tracking polarity is one for the groove-recordingsystem and a detection time required for detecting an optical disk ofthe groove-recording system can be shorten, whereby the start time whenthe unspecified optical disk is loaded can be shortened.

This invention makes it possible to omit the time required for arecording and reproduction apparatus to study the wobble polarity ofeach optical disk irrespective whether its recording system is thegroove-recording system or the land recording system. Further, therecording system of the information recording medium of the presentinvention can be easily judged by detecting whether or not the wobbleinformation is obtained from the wobble signals when tracking is carriedout under a predetermined polarity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an optical disk according to a firstembodiment of the present invention;

FIG. 2 is a schematic view of a laser master recording apparatus forproducing a master of the optical disk according to the first embodimentof the present invention;

FIG. 3 is a block diagram of a signal reproduction circuit of theoptical disk according to the first embodiment of the present invention;

FIG. 4 is a schematic view describing a groove polarity and a trackingsignal polarity of the optical disk according to the first embodiment ofthe present invention;

FIG. 5 is a schematic view of an optical disk according to a secondembodiment of the present invention;

FIG. 6 is a schematic view showing an example of wobble of a guidegroove formed in an information recording medium of groove-recordingsystem, according to a method of the present invention; and

FIG. 7 is a schematic view showing an example of wobble of a guidegroove formed in an information recording medium of land-recordingsystem, according to a method of the present invention.

Here, in FIGS. 1 to 7, the reference numbers represent the followingelements:

101 . . . substrate, 102 . . . recording film, 103 . . . overcoat, 104 .. . UV curable resin layer, 105 . . . PC sheet, 201 . . . laser, 202 . .. light regulator, 203 . . . deflector, 204 . . . beam expander, 205 . .. movable optical bench, 206 . . . master, 207, 208 . . . mirror, 209 .. . formatter, 210 . . . objective lens, 301 . . . optical disk, 302 . .. objective lens, 303 . . . mirror, 304 . . . photodetector, 305, 306 .. . preamplifiers, 307 . . . differential amplifier, 308 . . . trackingcircuit, 309 . . . wobble detecting circuit, 501 . . . substrate, 502 .. . second recording film, 503 . . . intermediate layer, 504 . . . firstrecording film, 505 . . . UV curable resin layer, 506 . . . PC sheet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention are described with reference tothe attached drawings.

First Embodiment

FIG. 1 shows a schematic view showing a construction of an optical diskaccording to the first embodiment of the present invention. The opticaldisk includes a substrate 101, a recording film 102 formed on a surfaceof the substrate 101, an overcoat layer 103 formed on a surface of therecording film 102 and a sheet 105 bonded to the overcoat layer 103through an adhesive layer 104. The substrate 101 is a substrate (orplate) which is formed by injection molding and has a guide groovewherein wobble information is recorded on its surface where therecording film 102 is formed. The substrate 101 has a thickness of about1.1 mm. The recording film 102 may be formed by, for example, a spincoat method using an organic dye. The overcoat layer 103 may be formedof a UV curable resin into a thickness of about 4 μm. The sheet 105 maybe a polycarbonate sheet (PC sheet) having a thickness of about 80 μm,and it may be bonded to the overcoat layer 103 by the adhesive layer 104of a UV curable layer.

A stamper gives the guide groove on the substrate upon the injectionmolding. That is, the stamper corresponds to a mold of the guide groove.The stamper may be produced using a master that is produced using alaser master recording apparatus.

FIG. 2 is a schematic view showing a construction of the laser masterrecording apparatus. A light emitted from a light source that is a laser201 (whose wavelength is 248 nm) is reflected on a mirror 207 and itsintensity is adjusted in a light regulator 202. The light is furtherreflected on a mirror 208 and deflected by a deflector 203. At thismoment, wobble information to be recorded is generated in a formatter209 and introduced in the deflector 203. The diameter of the lightdeflected by the deflector is adjusted in a beam expander 204, focusedby an objective lens 210 that is mounted in a movable optical bench 205,and applied to a master 206. A photoresist has been applied to thesurface of the master 206 which is irradiated with the light. The master206 is rotated on a spindle.

By changing the output polarity of the formatter 209, it is possible tochange the physical direction of the wobble recorded in the master 206,that is, the direction of the first wobble deviation (that is, whetherthe wobble starts its first wobble deviation towards the inner side orthe outer side of the disk). Therefore, the method for recording wobbleinformation of the present invention can be carried out by determiningthe recording system of the optical disk to be produced, selecting theoutput polarity of the formatter based on the determination, andproducing the master by means of this master recording apparatus, andproducing the stamper from this master, and forming the guide groove inthe surface of the substrate using this stamper.

In addition to reference frequency information which are used in orderthat a recording and reproduction apparatus synchronizes a linearvelocity, address information may be added to the wobble information bymixing signals (STW; Saw Tooth Wobbles) that are added while advancingor delaying the phase of a wave having double frequency relative to thereference frequency and signals having 1.5 times frequency of thereference frequency (MSK; Minimum Shift Keying).

In general, a Blu-ray Disc employs the groove-recording system. In thatcase, the wobble starts its first wobble towards the inner side of themedium, that is, the wobble starts at the inner side of the medium. Inother words, the wobble starts at a point where the wobble amount (or anamplitude) is maximum on the inner side of the medium. Such a wobble isas shown in FIG. 6. As shown in FIG. 6, in the case of thegroove-recording system, the starting point of the wobble is situated atthe inner side of the medium.

In the first embodiment, the output characteristic of the formatter 209is set so that the wobble starts its first wobble deviation towards theouter side of the disk, that is, the wobble starts at the outer side ofthe disk, considering that this disk employs the land-recording system.In other words, the output characteristic of the formatter 209 is set sothat the wobble starts at a point where the wobble amount is maximum onthe outer side of the disk. The wobble employed in the optical disk ofland-recording system is as shown in FIG. 7, and the start point of thewobble is situated at the outer side of the disk.

FIG. 3 shows a block diagram for detecting tracking signals and wobblesignals in a recording and reproduction apparatus at the time ofrecording information on and reproducing information from a fabricatedoptical disk. As shown in FIG. 3, a light reflected on an optical disk301 is focused by an objective lens 302 and reflected on a mirror 303and then introduced in a bisected photodetector 304. The section (ordividing) line is disposed perpendicular to movement of a radialdirection of the optical disk.

Outputs of channels of the photodetector 304 are amplified bypreamplifiers 305 and 306 respectively, become a differential signal ina differential amplifier 307, and the differential signal is input intoa tracking circuit 308 and an address detecting circuit 309.

FIG. 4 shows the relationship between push-pull tracking error signalscorresponding to the groove portions (G) and the land portions (L) whena spot of the light used for recording and reproduction traverses theguide groove. As shown in FIG. 4, the tracking error signals change as asubstantially sinusoidal waveform depending the period of the guidegroove. Although the error signals become zero at the center of thegroove portion and at the center of the land portion, the inclination atthe groove center is opposite to the inclination at the land center. Thereproduced wobble signals are generated by sifting the groove or theland purposefully and its polarity is the same as that of the trackingerror signals.

Therefore, in the case where a conventional master for an optical diskof land-recording system is used to produce an optical disk by, forexample, a mothering method so that a predetermined information isrecorded in land portions and the optical disk is used as one ofland-recording system, the polarity of the reproduced wobble signals isreversed. In the first embodiment, the wobble recording polarity isopposite to that employed in a medium of groove-recording system. Forthis reason, even if the tracking polarity is adapted to the landportion, the wobble signals whose polarity is opposite to the trackingpolarity are obtained. As a result, the polarity of reproduced wobblesignals from the optical disk of the first embodiment becomes identicalwith the polarity of those from the optical disk of groove-recordingsystem.

In lieu of the present invention, it might be considered that a methodfor reversing both of the wobble-signal polarity and the tracking-signalpolarity for groove-recording system by means of a common amplifier in arecording and reproduction apparatus when recording information on andreproducing information from the optical disk of land-recording system.This method does not require that the wobble shape for theland-recording system is reversal of the wobble shape for thegroove-recording system. However, the frequency band of the wobblesignals is significantly different from that of the tracking errorsignals (the former is several kHz and the latter is several tens kHz),a mechanism wherein the wobble signal and the tracking error signal areseparately managed using respective circuits designed specifically forrespective signals has an advantage that the property of the recordingand reproduction apparatus is maintained more easily compared to amechanism which reverse the polarities using the common amplifier. Inthe following, a method and an apparatus for recording information inand reproducing information from an optical disk wherein the wobbleinformation is recorded according to the method of the presentinvention.

The optical disk recording and reproduction apparatus of the presentinvention is used with its tracking polarity set for a groove-recordingsystem and a land-recording system, preferably for the groove-recordingsystem. When a conventional optical disk of groove-recording system isloaded in the recording and reproduction apparatus wherein the trackingpolarity is set for the groove-recording system and tracking is carriedout with an appropriate mechanism, wobble information is detected fromwobble signals. The detected information during this tracking may bepreferably address information included in the wobble information oranother characteristic information from which a location on the disk canbe identified. In the case of an optical disk of CLV (Constant LinearVelocity), the reference frequency signal may be detected as the wobbleinformation. When the wobble information is detected by setting thetracking polarity for the groove-recording system, the loaded opticaldisk is identified as one of groove-recording system. When the wobbleinformation is not detected, the tracking polarity is switched and thedetection of wobble information is carried out again. After switching,when the wobble information is detected, the loaded optical disk can beidentified as one of land-recording system.

The optical disk of the first embodiment can be identified as one beingof land-recording system according to the latter procedure.

As described above, the number of combinations of the tracking polarityand the wobble polarity is reduced by always detecting a wobble polarityof an optical disk under the same polarity in a recording andreproduction apparatus, whereby a start-up time is reduced upon loadingthe optical disk.

Second Embodiment

FIG. 5 is a schematic view showing a construction of an optical disk ofa second embodiment. This disk has two recording films. A secondrecording film 502 which is located further from a laser light may beformed on a substrate 501 using an organic dye by a spin-coat method.The substrate 501 is produced in the same manner as in the firstembodiment. Next, an intermediate layer 503 having a guide groove on itssurface is stacked. The guide groove formed in the intermediate layer503 is used to record information on and reproduce information from afirst recording film 504 that is located near to the laser light and italso may be formed using a stamper which is produced with a master. Thefirst recording film 504 whose main component may be a Te oxide film maybe formed on a surface of the intermediate layer 503 by a sputteringmethod. A polycarbonate sheet (PC sheet) 506 having a thickness of about65 μm is bonded to the surface of the second recording film 504 througha UV curable resin layer 505. A method for stacking the intermediatelayer 503 is described in Japanese Patent Kokai (Laid-Open) PublicationNo. 2003-203402(A) that is incorporated herein by reference.

In this optical disk, the recording system of the second recording film502 is land-recording system, and the recording system of the firstrecording film 504 is groove-recording system. Therefore, the wobbleguide groove is formed so that the wobbles starts its first wobbledeviation towards the outer side of the disk, that is, the wobble startsat the outer side of the disk, in the substrate 501 where the secondrecording film 502 is formed, while the wobble guide groove is formed sothat the wobble starts its first wobble deviation towards the inner sideof the medium, that is, the wobble starts at the inner side of themedium in the intermediate layer 503 for the first recording film 504.Each wobble guide groove for each recording layer is also formed byproducing a master that determines the shape of the guide groove with alaser master recording apparatus so as to record wobble information in apredetermined manner, and forming the substrate 501 or the intermediatelayer 503 by means of a stamper that is formed by the master.

This construction enables a two-layer optical disk to be obtained,wherein the tracking polarities of both recording layers are differentfrom each other, while the detecting polarity of the wobbles of bothrecording layers are the same.

Also for this optical disk, the tracking polarity of each recordinglayer can be easily identified according to the procedure fordistinguishing an optical disk of groove-recording system from anoptical disk of land-recording system with use of a recording andreproduction apparatus as mentioned above, in a manner as described inconnection with the first embodiment. Therefore, the start-up time isshortened by using this optical disk and a recording and reproductionapparatus which is provided with a mechanism for tracking each recordinglayer.

As the second embodiment, the two-layer optical disk is described whichhas two recording layers whose recording systems are different from eachother. Of course, a similar construction may be applied to an opticaldisk wherein the recording systems of the first and the second recordinglayers are the same. For example, in the case where the recordingsystems of the first and the second recording layers are bothgroove-recording system, the guide grooves are formed in the substrateand the intermediate layer so that wobbles start their first wobbledeviation towards the inner side of the medium. Further, a similarconstruction is applicable to a multi-layer optical disk having morethan two recording layers (for example, an optical disk having fourrecording layers). The optical disk having four recording layers has acombination wherein land portions or groove portions are used forrecording in each of the four recording layers. The combination may be,for example, a construction whereingroove-groove-groove-groove-recording systems are employed in therespective layers in this order from the side near to a laser light, ora construction wherein groove-groove-groove-land-recording systems areemployed in the respective layers in this order from the side near to alaser light.

In the first embodiment and the second embodiment, the physical polarityof the wobble is reversed on the optical disk. Alternatively, thepolarity of the reproduced wobble signals can be reversed by changing adepth of the guide groove. To this end, the depth of the guide groove orthe refractive index of a material for the recording layer may beadjusted so that difference between the optical path length of a lightreflected on a groove portion and the optical path length of a lightreflected on a land portion is not less than λ/2 and not greater than λ(λ: a wavelength of a light used for recording and reproduction).

As described above, by recording wobble information according to thepresent invention, there is an advantage that detection of the recordingsystem of an optical disk (that is, detecting whether the optical diskemploys a groove-recording system or a land-recording system) can beeasily made, and therefore the start-up time can be shortened uponloading the optical disk into the recording and reproduction apparatus.The present invention can be applied to various recordable disks, suchas a BD-R, a BD-RE, a DVD-R, and a DVD-RW. The present invention may bepreferably applicable to the BD-R on and from which information isrecorded and reproduced with a laser beam having a wavelength in ablue-violet region (specifically, about 405 nm).

The method for recording wobble information of the present invention ischaracterized in that the polarity of wobble information is made to bethe same irrespective of the recording system (a groove-recording systemor a land-recording system) of an information recording medium.Therefore, the present invention is advantageously applied particularlyto an information recording medium as to which both recording systemsare allowed (that is, coexisting) according to a specification (or astandard).

Further, the method and apparatus for recording and reproducinginformation of the present invention using the optical disk of thepresent invention employs a specific procedure and thereby makes itpossible to reduce the load on the recording and reproduction apparatuswhich load is added until the apparatus identifies the recording systemof the information recording medium. As a result, the recording andreproduction method and apparatus wherein the time required for start-upis reduced can be realized.

1. A method for recording information on and reproducing informationfrom an information recording medium wherein wobble information isrecorded by a method for recording wobble information of an informationrecording medium which comprises: selecting a recording system; andforming a guide groove having wobble information wherein the wobblestarts its first wobble deviation towards the inner side of the mediumin the case where the selected recording system is a groove-recordingsystem, or a guide groove having wobble information wherein the wobblestarts its first wobble deviation towards the outer side of the mediumin the case where the selected recording system is a land-recordingsystem, the method for recording and reproducing information comprisingdetecting whether the recording system of the medium is thegroove-recording system or the land-recording system by trackingpreviously a part of the guide groove and detecting the wobbleinformation to be detected from the part of the guide groove, and in thecase where the wobble information is not detected, reversing a trackingpolarity to detect the wobble information.
 2. The method according toclaim 1, wherein the information recording medium has a plurality ofrecording layers and said previous tracking is carried out for eachrecording layer so as to detect whether the recording system of eachrecording layer is the groove-recording system or the land-recordingsystem.
 3. The method according to claim 1, wherein the wobbleinformation to be detected is address information.
 4. The methodaccording to claim 1, wherein the information recording medium is amedium on and from which information is recorded and reproduced at aconstant linear velocity (CLV), and the wobble information to bedetected is synchronizing signal for maintaining the linear velocityconstant.